Group II-IV compound semiconductors are used as pigments utilizing their colors. Group II-IV compound semiconductors are extensively used especially because they exhibit various colors that depend on a combination of different metals. Specifically, Group II-IV compound semiconductors are used for applications, including solar cells, light receiving devices, and image recording devices, by using their semiconducting and photoconducting properties. Also, Group II-IV compound semiconductors are extensively used in EL devices, CRTs, and lighting equipment by using their fluorescence properties. A Group II-IV compound phosphor is generally prepared by reaction of a sulfurizing agent with a metal salt. Specifically, a process for the production of a phosphor in which a metal such as copper is doped as an activator is known (see Patent Citation 1). There is also known a process for the production of a phosphor in which two or more solutions containing raw materials of the phosphor are fed continuously and simultaneously to obtain the phosphor containing copper and manganese as luminescent metal centers (see Patent Citation 2).
However, it is difficult to uniformly dope a metal into a sulfide phosphor by using the conventionally known liquid phase synthetic processes, since in such processes a rate of sulfurization reaction by using a sulfurizing agent such as thioacetamide is not constant, and a composition of the resulting sulfide phosphor could vary over a reaction time. Thus, there have been questions about uniformity of concentration distributions of doped metals in sulfide phosphors obtained by the conventional liquid phase synthetic processes. Further, since sulfides are soluble in water, the sulfide of an expensive metal is dissolved in an aqueous solution and eluted off when used in a step of producing a sulfide phosphor. Thus, there has been a problem that it is difficult to efficiently dope a metal element into the resulting sulfide. Furthermore, a portion of a metal sulfide is hydrolyzed into a hydroxide and, further, into an oxide, which may be included as an impurity into a sulfide phosphor. This could lead to a decrease in efficiency of the phosphor.
Patent Document 1: JP 2005-132947
Patent Document 2: JP 2004-18709